In the field of vehicle automatic transmission, it is required that the vehicle transmission has a plurality of gears, high transmit power efficiently and compact structure, so that the vehicle has many advantages such as low fuel consumption and excellent driving performance, etc. Therefore, all the current vehicle automatic transmissions contain planetary gear sets and multiple-pieces friction type gear-shifting members such as clutches and brakes in order to increase the number of gears and to improve the efficiency of power-transmitting.
At present, various vehicle automatic transmissions in the market that have six forward gears and a reverse gear each has a single-row planetary gearset, a compound planetary gearset, three clutches and two brakes. The single-row planetary gearset is arranged in front of the compound planetary gearset. Two of the three clutches and the two brakes will be disposed between the two planetary gearsets. The other one of the three clutches will be disposed in front of the single-row planetary gearset. Alternatively, a friction component of the other clutch is disposed at the outer side of single-row type planetary gear and an actuating component is arranged in front of the single-row planetary gearset. Such an arrangement has been discussed in patent publications U.S. Pat. Nos. 7,125,360, 6,120,410 and EP0434525A1, etc. The main defect of such an arrangement is that structure in front of the compound planetary gearset is complicated and not compact enough since a gear-shifting member is provided in front or at the outer side of the single-row planetary gearset. In addition, the length of power-transmitting route is increased, and this has an influence on power-transmitting efficiency and thus on fuel consumption of vehicle.
Furthermore, no one-way clutch has been used in either the vehicle automatic transmission described in U.S. Pat. No. 7,125,360 or that described in EP0434525A1, thus the frequency of use of gear-shifting member for low speed gear is increased and the time for responding to a shift of a low speed gear becomes relatively longer, thereby the driving performance of vehicle is affected.